The present invention relates to a process for the preparation of polybenzoxazole or polybenzothiazole filaments and fibers.
In a typical process for preparing filaments or fibers of lyotropic liquid crystalline polybenzoxazole ("PBO") and polybenzothiazole ("PBT"), a dope of PBO or PBT polymer and an acid solvent is extruded through one or more orifices in a spinneret to form one or more dope filaments. The dope filaments are stretched or drawn to reduce the diameter of the filaments to a desired thickness. They are also coagulated by contacting them with a liquid which dilutes the solvent and is a non-solvent for the polymer. When multiple filaments are formed, they may be combined into one or more fibers either during or after coagulation. For obvious reasons, it is desirable to move the filaments or fibers through the process at speeds which maximize production, i.e., optimize line speed.
However, when a filament breaks prior to being combined to form a filament bundle or fiber, the process is disrupted until the line can be restrung. This is a time consuming operation which causes a loss of productivity. It is known that, in general, the faster the filaments or fibers move through the process (i.e., the higher the line speed), the more likely that filament breaks will occur. Slowing the line speed down makes line breaks less likely to occur, but decreases productivity accordingly.
It remains desirable to decrease the number of filament breaks at any line speed or increase the line speed without causing an unacceptable increase in the number of filament breaks.